Exposure to pathogens cause illness and even death to living organisms such as humans, animals and plants. There are numerous techniques used to diagnose pathogen infections and exposure.
One pathogen of importance to mammals is the bacterium, L. intracellularis. L. intracellularis is an obligate intracellular, Gram-negative rod, is the causative agent of proliferative enteropathy (Lawson and Gebhart 2000). L. intracellularis is viewed as an emerging cause of proliferative enteropathy in a variety of mammalian species (Drolet et al. 1996; Hotchkiss et al. 1996), including horses (Williams et al. 1996; Cooper et al. 1997; Frank et al. 1998; Brees et al. 1999), where the bacteria causes equine proliferative enteropathy (EPE).
Clinical signs of EPE, usually seen in weanlings or young yearlings (Frank et al. 1998; Brees et al. 1999; Lavoie et al. 2000; Schumacher et al. 2000; Frazer 2008), include anorexia, fever, lethargy, depression, peripheral edema caused by hypoproteinemia/hypoalbuminemia, weight loss, colic and diarrhea. In addition, thickened small intestine detected by abdominal ultrasound is considered highly suggestive of EPE when accompanied by compatible clinical signs. Commercially available ante mortem tests for EPE include fecal L. intracellularis-specific polymerase chain reaction (PCR) and the serum immunoperoxidase monolayer assay (IPMA), both of which have been adapted from their use in pigs where the tests are highly specific; sensitivity is reported to be high for the IPMA (Guedes et al. 2002a,b) but variable for faecal PCR (Herbst et al. 2003; Jacobson et al. 2004).
Although the epidemiology of EPE is uncertain, it is believed that transmission occurs through the ingestion of L. intracellularis-contaminated fecal material from wild or domestic animals (Pusterla et al. 2008b). While most cases of EPE typically occur in the fall and early winter (Frazer 2008; Page et al. 2011b), the reason for this seasonal predilection has not yet been determined. One possibility is the known susceptibility of weanlings to this infection and weaning typically occurs during this time of year (Frazer 2008). Another possibility would be that the environmental conditions at that time favor transmission by increasing exposure burdens.
Previous work on the detection of L. intracellularis-specific antibodies on specific farms demonstrated seroprevalences ranging from 33.8 to 45.5% on two California farms (Pusterla et al. 2008a) and up to 60% on a Kentucky farm (Page et al. 2011b), utilizing the IPMA method. A large scale, recent study, detailed within, found that seroprevalence on some equine farms actually approaches 100%.
Enzyme-linked immunosorbent assay (ELISA) for detection of L. intracellularis-specific antibodies have been previously developed for the pig and rabbit (Watarai et al. 2004; Boesen et al. 2005; Kroll et al. 2005; Wattanaphansak et al. 2008).